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P0300

P0300 on a 2015 Toyota Tacoma

P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.

Not your vehicle? See general P0300 info.

Most common causes on the 2015 Toyota Tacoma

Ranked from 100 NHTSA owner complaints filed for this vehicle.

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  1. 1

    Secondary Air Injection System (SAIS) Failure

    High severity

    The secondary air injection pump or switching valve fails, often causing the vehicle to go into limp mode. Look for codes P0418, P2445, or P2441 alongside sudden loss of power.

    Reported in 6 NHTSA complaints
  2. 2

    Rodent Damage to Wiring Harness

    Medium severity

    Rodents chew through the soy-based wiring insulation, causing electrical shorts and misfires. Inspect the engine bay, especially under the engine cover, for chewed wires or nests.

    Reported in 4 NHTSA complaints
  3. 3

    Faulty Spark Plugs

    Medium severity

    Worn or fouled spark plugs fail to ignite the air/fuel mixture properly. Inspect spark plugs for wear, carbon buildup, or incorrect gap.

    Common cause
  4. 4

    Defective Ignition Coils

    Medium severity

    A failing ignition coil cannot provide sufficient voltage to the spark plug, leading to misfires. Check for weak or absent spark and swap coils to see if the misfire moves.

    Common cause
  5. 5

    Vacuum Leaks

    Medium severity

    Unmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires. Inspect vacuum hoses and intake gaskets for cracks or leaks.

    Common cause
  6. 6

    Clogged or Failing Fuel Injectors

    Medium severity

    Restricted fuel flow prevents proper combustion in the cylinders. Perform a fuel injector balance test or check for proper injector pulse.

    Common cause

These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.

Common symptoms

  • Flashing or steady check engine light
  • Rough idle
  • Shaking under acceleration
  • Loss of power
  • Fuel smell from exhaust

What to check before replacing parts

1

Scan for cylinder-specific misfire codes

Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.

2

Inspect the spark plugs and coils

Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.

3

Check fuel trims for a vacuum leak

Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.

4

Verify fuel pressure

Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.

5

Compression / leak-down test if ignition and fuel check out

Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.

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Matching symptoms

Car Runs RoughFlashing Check Engine Light